Axial flow fan

ABSTRACT

An axial flow fan has structural stability, decreased deformation, decreased blade unbalance and low noise level because the blade distribution angle has an optimum clearance angle and uneven rate.

RELATED APPLICATIONS

The present application is based on, and claims priority from, KR Application Number 10-2006-0010535, filed Feb. 3, 2006; KR Application Number 10-2007-0001552, filed Jan. 5, 2007; and PCT Application Number PCT/KR2007/000234, filed Jan. 15, 2007, the disclosures of which are hereby incorporated by reference herein in their entireties.

TECHNICAL FIELD

The present invention relates to an axial flow fan, and more particularly, to an axial flow fan capable of promoting structural stability so as to decrease deformation and unbalance of a blade and accomplishing low noise level.

BACKGROUND ART

As shown in FIG. 1, an axial flow fan 10, which is used for cooling heat exchange medium passing an inside of a heat exchanger such as a radiator, a condenser and so on of a vehicle, is provided with a hub 20 coupled to a shaft 52 of a driving source 50 such as a motor, a plurality of blades 30 arranged radially at an outer circumference of the hub 20, and a fan band 40 for connecting tips of the blades 30 so as to prevent the blades from being deformed. The axial flow fan 10 is therefore rotated by rotational force transferred from the driving source 50 to the hub 20 and blows air in an axial direction by the blades 30.

A shroud 60 fixed to the heat exchanger is used to guide efficiently the air blown by the axial flow fan 10. The shroud 60 is formed so as to have a blowhole which is sized so that the axial flow fan 10 can be rotatably inserted therein, and support the motor 50 which is a driving source.

In the blade 30 of a conventional axial flow fan 10, as shown in FIG. 2, a leading edge LE which is an edge at a side of a rotational direction and a trailing edge TE which is an edge at an opposite side of the rotational direction have a backward sweeping angle inclined toward an opposite direction of the rotation as it goes from a root 32 of the blade connecting the blade 30 to the hub 20 to a center portion of the blade 30 and a forward sweeping angle inclined toward the rotational direction as it goes to a tip 34 of the blade connecting the blade to the fan band 40. Such change of the sweep angle is an important factor in performance of the axial flow fan, however it is known to be difficult to obtain satisfactory blowing efficiency and noise reduction effect. In consideration of above mentioned matter, improved axial flow fans have been proposed in Korean Patent Application Laid Open Nos. 2002-94183 and 2002-94184 by the present inventor.

As shown in FIG. 3 and FIG. 4, the former axial flow fan 10 a has a waveform structured blade 30 a, in which the sweeping angles of the leading edge LE and the trailing edge TE change alternately from a backward to a forward and from the forward to the backward as it goes from a root 32 a of the blade toward a tip 34 a of the blade. Further, a chord length CL is gradually increased as it goes from the root 32 a of the blade toward the tip 34 a of the blade. A reference symbol a denotes an angle of the blade 30 in relation to a horizontal line H. Reference symbols 20 a and 40 a denote the hub and the fan bend respectively.

As shown in FIG. 5 and FIG. 6, the latter axial flow fan 10 b has a waveform structured blade 30 b as same as the former, and a chord length CL (see FIG. 4) is also gradually increased as it goes from the root 32 b of the blade toward the tip 34 b of the blade 34 b. Further, the root 32 b of the blade has maximum backward sweeping angle and the tip 34 b of the blade has maximum forward sweeping angle. Reference symbols 20 b and 40 b denote the hub and the fan band respectively.

According to the axial flow fans 10 a and 10 b having the above mentioned waveform structured blades 30 a and 30 b respectively, an area between inflection points P1 and P2 located on a mid-chord line, which runs along middle points between the leading edge LE and the trailing edge TE, works as an area for dispersing air flow and thus prevent the air flow from being concentrated, thereby capable of increasing blowing efficiency and reducing noise compared to the axial flow fan shown in FIG. 1 and FIG. 2.

As shown in FIG. 7, in example, in the axial flow fan having the blade with above mentioned waveform structure, when assuming that an angle between two lines L1 and L2 which pass through a center C of the hub 20 b and middles C1 and C2 of each root 32 b of the blade, respectively, where the adjacent two blades 30 b and the hub 20 b come into contact, is a distribution angle A1 of the blade and a number of the blade is n, an equiangular distribution angle is defined as a case that the distribution angle becomes 360/n.

In addition, the distribution angle A1 of the blade can be moved by a predetermined angle in a rotational direction (+) or an opposite direction of the rotation (−) of the axial flow fan in the equiangular distribution angle, and at this time a range in which the angle can be increased or decreased is referred as a clearance angle B. In other words, it can be expressed by an equation: the distribution angle A1 of the blade=an equiangular distribution angle X the clearance angle B.

Meanwhile, U.S. Pat. No. 5,000,660 discloses an axial flow fan with a blade of an uneven structure in which curvatures from a root of the blade to a tip of the blade are different at least between two blades, and the axial flow fan is suggested for the purpose of increasing rigidity of a portion of the root of the blade and reducing noise in a portion of the tip of the blade. However, in the conventional axial flow fans with above described waveform structure, there are problems that unbalance is occurred when the axial flow fans rotate and satisfactory noise reduction effect can not be achieved if the clearance angle B is set to be excessively large.

DISCLOSURE Technical Problem

An object of the present invention is to provide an axial flow fan capable of promoting structural stability so as to decrease deformation and unbalance of a blade and accomplishing low noise level by determining a distribution angle of the blade with an optimum clearance angle and thereby determining uneven rate of the blade.

Technical Solution

An axial flow fan according to a preferred embodiment of the present invention includes a hub; a plurality of blades arranged radially in a circumference of the hub and having a sweeping angle of which direction changes alternately in an area between a root and a tip of the blade; and a fan band for connecting integrally the tips of the each blade; wherein when assuming that an angle between two lines which pass through a center of the hub and the middle of each root of the blade, respectively, where the adjacent two blades and the hub come into contact, is a distribution angle A1 of the blade, and an angle of an equiangular distribution angle is 360/n in the case that a number of the blades is n, the blades are arranged so that the clearance angle is in a range of 4° to 9°, while satisfying an equation: distribution angle (A1) of the blade=equiangular distribution angle±clearance angle.

According to a preferred embodiment of the present invention, it is preferable that the clearance angle is in the range of 6° to 7° In addition, it is preferable that when assuming that an angle between two lines which pass through a center of the hub and middles of each root of the blade, respectively, where the adjacent two blades and the hub come into contact is, a hub-side distribution angle of the blade, and an angle between two lines which pass through a center of the hub and middles of each tip of the two blades, respectively is a tip-side distribution angle of the blade, the hub-side distribution angle of blade and the tip-side distribution angle of blade are same.

In addition, the blade has the sweeping angle which changes gradually as it goes from the tip of the blade having a forward angle to the root of the blade having a backward angle and connected to the hub and a plurality of flow dispersing areas between the forward angle area of a side of the tip of the blade and the backward angle area of a side of the root of the blade, in which a direction of the sweeping angle is alternately reversed.

At this time, it is preferable that the blade has a leading edge extending from the tip of the blade to the root of the blade, and a direction of a sweeping angle of the leading edge changes gradually from a maximum backward angle at the root of the blade to a maximum forward angle at the tip of the blade, wherein the direction of the sweeping angle is reversed from the backward angle at a side of the root of the blade to a forward angle, then reversed to a backward angle and reversed again to a forward angle so as to be connected to a forward angle at a side of the tip of the blade. Further, it is preferable that the blade has a trailing edge extending from the tip of the blade to the root of the blade, and a changing pattern of a sweeping angle of the trailing edge is as same as that of the leading edge.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:

FIG. 1 is an exploded perspective view illustrating an example of a conventional axial flow fan and shroud assembly.

FIG. 2 is a partial front view illustrating the conventional axial flow fan.

FIG. 3 is a front view illustrating another example of a conventional axial flow fan.

FIG. 4 is a sectional view of a blade for defining a chord.

FIG. 5 is a perspective view illustrating yet another example of a conventional axial flow fan.

FIG. 6 is a partial front view illustrating the axial flow fan shown in FIG. 5.

FIG. 7 is a partial front view for explaining distribution angle of a blade in the axial flow fan shown in FIG. 5.

FIG. 8 is a front view of a preferred embodiment of an axial flow fan according to the present invention.

FIG. 9 is a partial front view for explaining a structure of a blade in the axial flow fan shown in FIG. 8.

FIG. 10 to FIG. 15 are graphs comparatively showing noise levels according to frequency in relation to the axial flow fan according to the fan of FIGS. 8 and 9 and the conventional axial flow fan.

FIG. 16 is a graph showing variation pattern in overall noise according to variation of a clearance angle.

LISTING OF THE MAIN ELEMENTS OF THE DRAWINGS

-   110: hub -   120: blade -   122: root of the blade -   124: tip of the blade -   130: fan band -   A1: distribution angle of the blade -   C: center of the hub -   C1, C2: middle of the root of the blade which is in contact with the     hub -   L1, L2: line crossing a center of the hub and the middle of the root     of the blade -   D: flow dispersing area -   S1, S2: flow concentrating part -   r₁₁, r₁₂, r₁₃: first, second and third inflection points

DETAILED DESCRIPTION OF THE DRAWINGS

Hereinafter, the preferred embodiments of the present invention are described in detail with reference to accompanying drawings.

FIG. 8 is an illustration of an axial flow fan according to a preferred embodiment of the present invention. The axial flow fan 100 includes a hub 110; a plurality of blades 120 radially arranged at a circumference of the hub 110 and having a sweeping angle of which direction changes alternately in an area between a root 122 of the blade and a tip 124 of the blade; and a fan band 130 for connecting integrally the tips 124 of the each blade 120. In the present embodiment, the illustrated axial flow fan 100 has 9 blades 120.

In accordance with an aspect of the present invention, when assuming that an angle between two lines L1 and L2 which pass through a center C of the hub 110 and middles C1 and C2 of each root 122 of the blade, respectively, where the adjacent two blades 120 and the hub 110 come into contact, is a distribution angle A1 of the blade, a range of an angle by which the distribution angle A1 of the blade is movable in a rotational direction (+) or an opposite direction of rotation (−) of the axial flow fan 100 is a clearance angle, and a number of the blade is n, an equiangular distribution, representing an interval by which the blades are arranged, can be defined by 360/n.

In other words, the blades 120 can be exemplary arranged in interval of 40°, an actual angular distribution of the blade 120 can be moved in the rotational direction (+) or the opposite direction of rotation (−) of the axial flow fan 100 by a predetermined angle in the range of the clearance angle. The distribution angle A1 of the blade 120 can be expressed by an equation: a distribution angle A1 of the blade=an equiangular distribution angle±a clearance angle, and the clearance angle is preferably in a range of 4° to 9° and more preferably in a range of 6° to 7°.

Further, when assuming that an angle A1 r between two lines L1 and L2 which pass through center C of the hub 110 and the middle C1 and C2 of each root 122 of the blade, respectively, where the adjacent two blades 120 and the hub 110 come into contact is a hub-side distribution angle of the blade and an angle A1 t between two lines L3 and L4 which pass through center C of the hub 110 and the middle C3 and C4 of each tip 124 of the two blades 120, respectively is a tip-side distribution angle of the blade, it is preferable that the hub-side distribution angle A1 r of blade and the tip-side distribution angle A1 t of blade are same.

FIG. 9 is a partial front view for explaining a structure of the blade in the axial flow fan of the present invention shown in FIG. 8. In the blade of FIG. 9 are shown a leading edge LE, a trailing edge TE and a mid-chord line ML defined as a line which runs radially along middle points between the leading edge LE and the trailing edge TE. As shown, in the axial flow fan according to the present invention, the leading edge LE of the blade 120 has a sweeping angle of which direction is gradually changes from the maximum backward sweeping angle at the root 122 of the blade to the maximum forward sweeping angle at the tip 124 of the blade in a full section between the root 122 of the blade and the tip 124 of the blade. Further, the leading edge LE has a flow dispersing area D, which is a small section starting from a first inflection point r₁₁, at which the direction of the sweeping angle is changes from backward to forward, passing through a second inflection point r₁₂, at which the direction of the sweeping angle is changes again from forward to backward, and reaching to a third inflection point r₁₃, at which the direction of the sweeping angle is changes again from backward to forward.

In other words, the leading edge LE of the blade 120 is formed such that the direction of the sweeping angle gradually changes from backward at a side of root 122 of the blade in an order of forward, backward and forward, and finally to forward at a side of the tip 124 of the blade between a backward area of the side of the root 122 of the blade 120 and a forward area of the side of the tip 124 of the blade 120.

Further, as shown, the trailing edge TE of the blade 120 is also formed as same pattern as the leading edge LE, that is, such that the direction of the sweeping angle gradually changes from backward at a side of root 122 of the blade in an order of forward, backward and forward, and finally to forward at a side of the tip 124 of the blade between the backward area of the side of the root 122 of the blade 120 and the forward area of the side of the tip 124 of the blade 120.

As described above, the flow dispersing area D forms two flow concentrating parts S1 and S2 at which flows are concentrated to a side of the trailing edge TE and thus acts to lessen greatly concentration of the flow, thereby increasing a blowing efficiency relative to power consumption and greatly reducing noise generation.

FIG. 10 to FIG. 15 are graphs comparatively showing noise levels throughout frequencies in the case that the clearance angle is 4° to 9° according to the present invention. As shown in FIG. 10 to FIG. 15, test to the axial flow fans according to the present invention (the first and second embodiments) and the conventional axial flow fan under the condition of same voltage showed that the axial flow fans according to the present are much lower in noise level than the conventional one. The axial flow fans according to the present invention has much air flow rate in a low rpm and test to the axial flow fans according to the present invention and the conventional axial flow fan under the condition of same air flow rate showed that the axial flow fans according to the present are much lower in noise level, rpm and voltage than the conventional one.

In the graphs of FIG. 10 to FIG. 15, noise level of even fan is denoted with black solid line and noise levels of each uneven fan are denoted with gray dotted lines. In FIG. 10 to FIG. 15, it may be clearly noted that a value of noise peak of the uneven fan is much lower than that of the even fan.

Table 1 lists data of variation in overall noise according to the clearance angle and FIG. 16 graphically shows the data of table 1.

TABLE 1 Clearance Angle (°) Overall Noise (dB)  0 67.9  1 67.7  2 67.6  3 67.8  4 67.0  5 66.6  6 66.3  7 66.6  8 66.5  9 66.7 10 67.2 11 67.3 12 67.5 13 67.4 14 67.9

In the above table 1 and FIG. 16, the case that the clearance angle is 0° means the case of the even fan, i.e. the case that blades are exactly arranged in an equiangular distribution (distribution angle of blade=equiangular distribution angle). FIG. 16 shows clearly a tendency, in which the noise is very high in the case that the distribution angle of blade is the equiangular distribution angle, that is, the clearance angle is 0°, and the noise is gradually reduced with increase of the clearance angle while the noise is increased again if the clearance angle passes over a specific value. As shown, it will be known that the noise is clearly reduced in the case that the clearance angle is 4° to 9° than in the case of the even fan, particularly noise reduction effect is maximized in the case that the clearance angle is 6° to 7°.

INDUSTRIAL APPLICABILITY

With the above described axial flow fan according to the present invention, it is capable of promoting silence operation of an apparatus which employs an axial flow fan as noise can be greatly reduced compared to the conventional axial flow fan by determining the distribution angle of the blade 120 with an optimum clearance angle. Further, blowing efficiency and noise reduction effect can be much increased by adjusting the clearance angle as well as forming the flow dispersing area on the blade.

In addition, as the axial flow fan according to the present invention can generate much air flow rate even in low rpm compared to the conventional one, it is capable of promoting structural stability and thus increasing durability of the axial fan. 

1. An axial flow fan comprising a hub, a plurality of blades arranged radially in a circumference of the hub and having a sweeping angle of which direction changes alternately in an area between a root and a tip of the blade, and a fan band for connecting integrally the tips of the each blade, wherein, a distribution angle A1 of the blade is an angle between two lines which pass through the center of the hub and the middle of each root of the blade, respectively, where the adjacent two blades and the hub contact each other, and an angle of an equiangular distribution angle is 360/n, where n is the number of blades is n, the blades are arranged so that the clearance angle is in a range of 4° to 9°, while satisfying the equation: distribution angle of the blade=equiangular distribution angle±the clearance angle.
 2. The axial flow fan according to claim 1, wherein the clearance angle is in the range of 6° to 7°.
 3. The axial flow fan according to claim 2, wherein, an angle between two lines which pass through the center of the hub and the middle of each root of the blade, respectively, where the adjacent two blades and the hub come into contact, is a hub-side distribution angle of the blade, and an angle between two lines which pass through the center of the hub and the middle of each tip of the two blades, respectively is a tip-side distribution angle of the blade, the hub-side distribution angle of the blade and the tip-side distribution angle of the blade are same.
 4. The axial flow fan according to claim 3, wherein the blade has a sweeping angle which changes gradually as it goes from the tip of the blade having a forward angle to the root of the blade having a backward angle and connected to the hub and a plurality of flow dispersing areas between the forward angle area of a side of the tip of the blade and the backward angle area of a side of the root of the blade, in which the direction of the sweeping angle is alternately reversed.
 5. The axial flow fan according to claim 4, wherein the blade has a leading edge extending from the tip of the blade to the root of the blade, and the direction of the sweeping angle of the leading edge changes gradually from a maximum backward angle at the root of the blade to a maximum forward angle at the tip of the blade, wherein the direction of the sweeping angle is reversed from the backward angle at a side of the root of the blade to a forward angle, then reversed to a backward angle and reversed again to a forward angle so as to be connected to a forward angle at a side of the tip of the blade.
 6. The axial flow fan according to claim 4, wherein the blade has a trailing edge extending from the tip of the blade to the root of the blade, and a changing pattern of a sweeping angle of the trailing edge is the same as that of the leading edge.
 7. The axial flow fan according to claim 1, wherein, an angle between two lines which pass through the center of the hub and the middle of each root of the blade, respectively, where the adjacent two blades and the hub come into contact, is a hub-side distribution angle of the blade, and an angle between two lines which pass through the center of the hub and the middle of each tip of the two blades, respectively is a tip-side distribution angle of the blade, the hub-side distribution angle of the blade and the tip-side distribution angle of the blade are same. 